This invention relates generally to emission control strategies for compression ignition engines and, more particularly, to a combustion strategy that controls emissions generated by compression ignition diesel engines.
Diesel engine exhaust is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (CO), carbon dioxide (CO2), unburned hydrocarbons (HC) and nitrogen oxides (NOx). Additionally, diesel engine exhaust contains particulate matter (PM). Soot is a solid, dry, carbonaceous material and is one component in total particulate matter (TPM). Soot contributes to visible emissions in diesel exhaust. As diesel engines operate with an excess of combustion air (lean exhaust), such engines generally have emissions of CO and gas phase HCs that are below the limits set by the Environmental Protection Agency (EPA). In recent year, however, emissions from diesel engines have been under increased scrutiny and standards, especially for particulate emissions, have become stricter.
There is increasing pressure on the railroads to reduce the emissions of the current fleet. In response, several railroads have agreed to significantly improve emission levels of current locomotives to achieve a fleet average of U.S. EPA Tier II level by 2010. At present, over 85% of the North American railroad fleet was built prior to the year 2000. These locomotives have not yet reached the end of their useful life but must eventually meet the US EPA Tier 0 standards and potentially even lower emissions levels. For locomotives operating in California, NOx emissions levels must be reduced to meet the Tier II EPA requirements discussed above. The railroad companies that own these older locomotives stand to incur a heavy loss by retiring them prematurely or paying fines unless the locomotives can be modified to meet lower emissions levels. Accordingly, there is a need in the art to provide a more effective method and system for emission control of diesel engines without requiring much change in their engineering design.